This proposal concerns the development of a new technology for administering drugs and other biologically active fluids to living cells and tissues in vitro or in vivo. The new technology is based on ink-jet printing, in which computer-controlled jets are used to dispense picoliter droplets of fluids in highly precise temporal and spatial patterns. Our company, Microfab, has developed Micro- Jet fluid dispensers for numerous industrial and manufacturing applications; here we seek funds to develop a Micro-Jet instrument for biomedical research. The Micro-Jet has many potential uses in biomedical research, including (i) dispensing solutions for microanalysis/microassay; (ii) placing reagent microspots on tissue for microhistochemistry; (iii) precisely controlled delivery of drugs in picoliter to microliter amounts to living cells and tissues. The present work will test Micro-Jet techniques for focal application of drugs onto living tissue in vitro. Picoliter aliquots of drug will be "fired" from the remotely-aimed Micro-Jet (positioned above a brain tissue slice) onto preselected regions of the tissue slice, and effects will be monitored by recording neuronal action potentials. Future applications are envisioned in which brain tissue is rapidly "scanned" for drug-sensitive receptors by computer-controlled aiming of the Micro-Jet at sequential discrete loci.